NSURLSession断点续传

1 对 NSURLSesiion 的基本认识

      NSURLSesiion是苹果在iOS7推出的一个类，它具备了NSURLConnection所具备的方法，同时也比它更强大。苹果推出它的目的大有取代NSURLConnection的趋势或者目的。

2 实现原理



3 代理方法

/* Sent when a download task that has completed a download. The delegate should
* copy or move the file at the given location to a new location as it will be
* removed when the delegate message returns. URLSession:task:didCompleteWithError: will
* still be called.
*/
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location;

@optional
/* Sent periodically to notify the delegate of download progress. */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didWriteData:(int64_t)bytesWritten
totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

/* Sent when a download has been resumed. If a download failed with an
* error, the -userInfo dictionary of the error will contain an
* NSURLSessionDownloadTaskResumeData key, whose value is the resume
* data.
*/
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes;